Ventilation, i.e., the removal of excess heat and moisture from within the footwear, is one of the few areas where performance of modern footwear that remains unsatisfactory. Although there is an extensive prior art concerning the forced air ventilation of footwear, typical forced air ventilation systems are costly and difficult to manufacture, have poor durability, or are otherwise incapable of circulating a sufficient amount of air to cool the wearer's foot effectively.
To reduce the cost and difficulty in footwear having a forced air ventilation system, improvements have been proposed in which the entire ventilation system is incorporated in a removable insole. Such ventilating insoles are disclosed in U.S. Pat. No. 3,331,146 (disclosing a chamber in the heel of an insole with duct leading into the front of foot and a second duct rising above the foot-enclosing upper); U.S. Pat. No. 4,776,110 (disclosing an insole with a chamber in the heel, multiple distribution channels, and an air guide for exchanging air through the side of the foot-enclosing upper); U.S. Pat. No. 5,068,981 (disclosing a heel chamber incorporating a mechanical spring and ducts configured to vent through the peripheral walls of the foot-enclosing upper); U.S. Pat. No. 5,195,254 (disclosing a molded insole and an assisting "blast device"); and U.S. Pat. No. 5,333,397 (disclosing a kidney-shaped air chamber position at the rear and inner periphery of the insole). Such insoles with ventilation system, however, have several intrinsic disadvantages such as:
(1) the volume of air that can be circulated by an insole device is severely limited by the thickness of the insole; PA1 (2) the periodic compression of the insole pump requires the wearer's foot to move vertically relative to the interior sides of the footwear, resulting in friction, irritation, and possibly blisters; PA1 (3) the re-circulation of the air contained within the footwear provides little long-term benefit, and the process itself may even cause the interior temperature to rise; PA1 (4) insoles adapted to exchange air with the external environment are complex and often affect the design, manufacture, and aesthetic aspects of the footwear; and PA1 (5) the space and material limitations of the insole design result in a rapid degradation of their cushioning and air-pumping capabilities.
Another footwear ventilation system embeds the ventilation system in the sole structure of footwear with relatively thick, resilient midsole components. Examples include U.S. Pat. No. 1,660,698 (disclosing a cup-shaped cavity in the heel of footwear partially filled with a resilient material so as to form a toroidal pumping chamber); U.S. Pat. No. 3,973,336 (disclosing an air chamber in the heel of a footwear that is squeezed between the outsole and a press member when the footwear is flexed); U.S. Pat. No. 5,515,622 (disclosing an air bag in the heel of a footwear with a volume of about 20 cubic centimeters (cc)); U.S. Pat. No. 5,606,806 (disclosing a collapsible heel cavity with a volume of 75 cc); and U.S. Pat. No. 5,010,661 (dislosing a unidirectional ventilation sytem in which air is pumped into a cavity in the heel of the shoe, and then pumped out through outlets in the front part of the shoe).
All of these embedded systems provide some form of fluid connection between the system and the interior of the foot-enclosing upper via passages through the footbed and insole. Although placement of the ventilation system in the sole structure solves many of the problems inherent in the insole approach, it creates new problems as well. For example, there are still significant limitations on the amount of air that can be pumped. On one hand, a sole structure that is too stiff limits compression of air chamber and thereby restricts effective air circulation. One the other hand, a softer sole structure that enables air chamber compression provides little cushioning.
To solve the cushioning problems, additional components are often added to insure that the sole structure continues to perform all of its normal functions. For instance, additional modifications such as increasing the resilience of the air chamber, increasing the resilience of the surrounding materials, or adding a spring mechanism, are required to reinflate the air chamber. Another solution is to increase cushioning by restraining airflow within the ventilation system. This approach, however, reduces the cooling effect and increases energy losses and noise problems. Attempts to have both cooling and cushioning effect in a footwear have increased the complexity and cost of the ventilation system. Furthermore, the varying stiffness of the various components in a footwear often lead to local high-stress areas that cause components to breakdown and separate.
As described above, there is still an unsatisfied need for a footwear with a ventilation system that is inexpensive and easy to manufacture, and capable of pumping sufficient air to effectively cool the wearer's foot. The design of the ventilation system must also not compromise cushioning, durability, stability, and/or the aesthetic aspects of the footwear.